The present invention relates to a method for controlling the operation of a satellite and, more particularly, to a method for controlling the operation and consumption of propellant of a satellite near the end of its useful life.
Spacecraft propulsion systems typically use at least two tanks that store propellant therein. The propellant is used to maintain the satellite orbit due to various perturbations in space. A small amount of propellant is required to maintain an orbit. When a satellite nears the end of its propellant, the satellite may be placed in a graveyard orbit.
A standard method for determining the amount of remaining propellants on a spacecraft in orbit is to keep track of the propellant by bookkeeping. That is, keeping track of the burn times and thus deducing the amount of propellant used which can be subtracted from the propellant loaded prior to launch. This method is typically no more accurate than one percent of the loaded propellant. This amount may be equivalent to several months of station keeping. Because the spacecraft is deorbited several months before the end of its useful life, potentially millions of dollars in revenue are lost.
Another method for performing determining the amount of propellant is described in the parent application. The method described therein set forth a method that empties a tank. In some situations, it may not be desirable to empty a tank.
The present invention proposes a method that can be used on existing and future spacecraft to predict the amount of propellant therein without incorporating expensive fuel gauge type devices and without emptying a fuel tank.